Do na.locf on the data before sending for lmAMM, since it created an invalid zoo object. Did the same for other models to keep things consistent. Will be removed in the future.

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/eventstudies@399 edb9625f-4e0d-4859-8d74-9fd3b1da38cb